This invention relates generally to an optical sensing method and device therefore. More particularly, this invention relates to a new and improved optical sensing method and device which incorporates a suitable optical sensor system, preferably a fiber optic system with an environmental sensitive polymeric material which undergoes changes in optical properties in response to environmental changes. This novel polymeric/optical sensor combination will accurately and at times reversibly measure and detect temperature, humidity, pressure, position, radiation, flow, strain/stress, light, color, electric field, and a plurality of other properties with respect to changes in the environment.
Optical sensors and particularly fiber optical sensing devices have found increasing use and acceptance. Recently, fiber optics technology has undergone phenomenal growth in various facets of industry, medicine, and communications. In fact, new applications for fiber optics are emerging daily for a variety of reasons. For example, unlike conventional wire transmission devices, light transmitting fiber optic systems employing glass, plastic or similar fibers are immune to radio frequency interference and electromagnetic interference. They are inert to hazardous or extreme environments and are not affected by temperatures from cryogenic levels to several hundred degrees Centigrade. Also, difficult to reach and normally inaccessible areas are easily penetrated by the small size and flexibility of fiber optic systems.
As a result, fiber optics are finding great success in the process control and automation areas. Since the fibers do not conduct electricity, they are immune to electrical interference, require no expensive shielded cable and provide very high accuracy. This high accuracy translates into improved reliability over mechanical and/or electronic sensors.
As already discussed, fiber optic systems have shown great promise in the fields of sensors and detectors for sensing a multitude of environmental and other properties. While some of these properties can be detected with known and conventional fiber optical devices, certain environmental phenomena require combining fiber optics with other secondary materials or devices. Accordingly, U.S. Pat. No. 4,215,285 describes a device for measuring a plurality of environmental properties which combines fiber optic techniques with a variety of phosphor compounds. For example, when measuring temperature, the object or environment to be measured is provided with a layer of phosphor material that when excited to luminescence emits detectable radiation within two or more distinct wavelength ranges that are optically isolatable from one another. The relative intensity of the emission in these wavelength ranges will vary in a known manner as a function of the temperature of the phosphor. The complexity of detecting these distinct wavelengths creates certain drawbacks in the phosphor detector devices. Accordingly, the complexity results in very high manufacture costs which severely limits the practical use of the fiber optics/phosphor system.
Similarly, other types of sensing devices which have combined both an optical system and other secondary materials or devices have been utilized such as bimetallic strips where the reflected light will be a function of the movement of the strip with temperature, piston movement resulting from gas or liquid expansion in an enclosed chamber, and flexible diaphragm movement for pressure measurements. Unfortunately, all are plagued with a variety of problems. Chief among these problems is a complexity of design and manufacture which results in high labor costs as well as greater chance for component malfunction.
Obviously, a material which can be combined with a fiber optics system and which can observe, monitor and detect environmental (i.e., temperature, humidity, pressure, etc.) changes during continual operations with accurate reproducibility would be highly advantageous. One well known class of materials which is capable of changing its optical properties as a function of temperature, humidity, etc., is organic polymeric materials, especially semicrystalline, crosslinked, high strength amorphous polymers, and such polymers with additives. For example, during heating and cooling, semicrystalline polymers undergo a well-known predictable and repeatable transformation of optical properties. Similarly, when exposed to solvent materials, polymers often undergo crazing which also affects the optical properties of the polymer. Surprisingly, despite these desirable and peculiar characteristics of polymers, the use of polymeric materials as a sensing medium in a fiber optic light transmitting assembly has heretofore not been practiced in the prior art.
Accordingly, it is a principle object of the present invention to provide a sensing medium to be used in conjunction with a suitable optical sensor system which overcomes the deficiencies of the prior art.
It is another object of the present invention to provide an organic environmental sensitive polymeric material, which undergoes changes in optical properties in response to environmental changes, in combination with a fiber optic light transmitting assembly to sense and/or detect changes in certain environmental properties.
It is still another object of the present invention to provide a semicrystalline and crosslinked polymeric material, which undergoes a transition in light or wave energy transmission at its melting point for use in indicating temperature change in optical sensors, preferably fiber optical sensors.
It is still another object of the present invention to combine a suitable environmental sensitive polymeric material with an optical sensor, preferably a fiber optical sensor to measure and detect changes in the relative humidity of the surrounding environment.
It is yet another object of the present invention to combine a suitable polymeric material in combination with an optical sensor, preferably a fiber optical sensor, to measure and detect changes in a multitude of environmental properties including, but not limited to, pressure, stress/strain, solubility, radiation, direction, position, flow, sound, acceleration, light, color and electrical field.